A review of elasmobranch catch-and-release science: synthesis of current knowledge, implications for best practice and future research directions

Abstract Until relatively recently commercial fisheries have been considered the main driving factor for elasmobranch population declines. However, this belief has begun to shift with the realization that recreational elasmobranch catches may equal or exceed commercial catches in some regions. Many recreational angling fisheries for elasmobranchs involve high participation in catch-and-release angling practices. However, high release rates may not necessarily equate to high survival rates. Therefore, to assist accurate assessment of the potential impact of recreational angling on elasmobranchs, we attempted to summarize and integrate currently available information on specific risk factors associated with recreational angling, alongside associated mortality rates, as well as information on angler behaviour as it relates to identified risk factors. We categorized the major angling-related effects into two groups: injury-induced effects; and biochemical disruption-induced effects; providing a summary of each group and outlining the main lethal and sub-lethal outcomes stemming from these. These outcomes include immediate and delayed post-release mortality, behavioural recovery periods (which may in-turn confer increased predation risks), chronic health impacts and capture-induced parturition and abortion. Additionally, we detailed a range of angling practices and equipment, including hook-type, hook removal and emersion (i.e. air exposure), as well as inter- and intra-specific factors, including aerobic scope, respiratory mode, body size and species-specific behaviours, which are likely to influence injury and/or mortality rates and should therefore be considered when assessing angling-related impacts. We then utilized these data to provide a range of actionable recommendations for both anglers and policymakers which would serve to reduce the population-level impact of recreational angling on these enigmatic animals.


Introduction
Commercial fisheries are traditionally considered to be the main global threat to elasmobranch populations (e.g.Field et al., 2009;Campana, 2016;Dulvy et al., 2021), but there is now a growing appreciation of the potential impacts of recreational angling for these species (e.g.Gallagher et al., 2017a).In some cases, recreational shark catches may even exceed commercial ones (NOAA, 2014), with more than 66 million sharks caught by recreational anglers between 2005 and 2015 along the U.S. Atlantic coast alone, including 1.2 million individuals of prohibited species (Kilfoil et al., 2017).Globally, elasmobranchs are estimated to represent approximately 5% to 6% of marine recreational angling catches (Freire et al., 2020).Given the growing appreciation of the recreational angling sector's potential impact, in recent years there has been a steady regulatory push towards catchand-release fishing within the recreational angling community (e.g.Kneebone et al., 2013), in many cases accompanied, or preceded, by a voluntary shift towards such methods by anglers (Gallagher et al., 2017a).
When considering the negative impacts of angling it should be noted that many anglers hold conservation-oriented views (Shiffman et al., 2017) and may participate in research and conservation activities (e.g.Drake et al., 2005;Neat et al., 2015).Additionally, anglers often fund conservation and research efforts either directly or indirectly (e.g.Barnett et al., 2016;Cooke et al., 2016) and, as noted previously, may voluntarily participate in catch-and-release angling, often in conjunction with practices believed to best promote animal welfare (Gallagher et al., 2017a).However, it should be stated that even widespread application of catch-and-release angling does not equate to an absence of negative effects as, even under ideal conditions, a proportion of fish could be expected to die from biochemical disruptions and/or injuries related to fishing (Cooke and Schramm, 2007).Critically, while the impacts of catch-and-release angling are well documented for many recreationally important teleosts, such as salmonids (Cooke et al., 2013) and cod (Weltersbach and Strehlow, 2013), these have only more recently come into focus for elasmobranchs and hence there are still important knowledge gaps which remain unresolved.
Recently an increasing number of studies have focussed on the conservation and animal welfare implications of catchand-release activities within recreational angling fisheries where elasmobranchs are either the primary target or are commonly caught.Studies to date have primarily been centred around classifying the nature and severity of the associated injuries, biochemical disruptions and subsequent post-release behavioural responses in various elasmobranch species to catch-and-release fishing (e.g.Kneebone et al., 2013;Lavender et al., 2022;Shea et al., 2022), alongside the associated mortality risks (e.g.Kneebone et al., 2013;Sepulveda et al., 2015;Anderson et al., 2021).Several studies have also investigated the effects of specific angler behaviours or fishing equipment under the overarching umbrella of best practice catch-and-release, with the core aim of reducing recreational angling-related impacts (e.g.French et al., 2015a;Mohan et al., 2020;Weber et al., 2021).
Here we attempt to synthesize research to-date on the various impacts of catch-and-release fishing for elasmobranchs, along with the associated mortality risks and sub-lethal consequences of such impacts, with an additional focus on the development of evidence-based best practice guidelines for the capture and release of these species.We provide a broad overview on the current state of research, highlighting current limitations of such research and key knowledge gaps, alongside recommendations for both future avenues of research and angling practices.

Materials and Methods
Literature searches were carried out using Google scholar and within the Wiley, Elsevier and Springer online research databases using the search terms outlined in Table 1, with all possible search term combinations tested.The first 200 results from each search were individually assessed for their relevance to the research topic and included where relevant.In some searches, due to overlap with unrelated research areas, it was also necessary to exclude additional terms to better refine search results.For any studies which were of primary relevance (i.e.those which directly addressed impacts of catchand-release angling), both the cited material within these and any subsequent literature citing the original study were also reviewed for their relevance.This approach was considered to give the greatest likelihood of identifying publications directly addressing the main research area, as well as those which may have only provided relevant information incidentally.

Overview of Catch-and-Release Science
A range of animal welfare implications are inevitably associated with recreational catch-and-release angling, given the inherent injury and stress associated with the process of capture via hook and line, handling (often including removal from the water and exposure to air) and release (Figure 1).These impacts can be broadly categorized as resulting from the physical injury and/or the biochemical disruptions associated with this process, the ultimate consequences of which may range from relatively minor short-term impairments to mortality (both direct and indirect).
Broadly in line with the above, the methods investigated in most catch-and-release studies can be classified into three groups: 1. physical injury/condition studies, in some cases also including assessments of reflex impairment.2. biochemical studies, often involving measurements of blood parameters at either the point of capture or release 3. movement studies, which generally seek to assess behavioural recovery periods or post-release mortality rates based on data-logging or telemetry devices.
It is important to note that several studies have combined these methods, with combinations of blood parameters, reflex impairments and/or physical condition used as predictive measures for post-release mortality.

Physical injury-related impacts
Perhaps the most obvious impact of any form of hook and line fishing is the injury caused by the fishing hook(s) to the animal (Figure 1).These injuries can vary in severity from superficial injuries when animals are hooked in the outer portions of the mouth (Begue et al., 2020;Keller et al., 2020Keller et al., , 2021)), to severe injuries caused by gill-hooking (French et al., 2015a); internal 'gut-hooking' (Borucinska et al., 2002(Borucinska et al., , 2001;;Kilfoil et al., 2017); or tail hooking (Heberer et al., 2010;Sepulveda et al., 2015).Such events may also increase the difficulty of hook removal, leading to retention of fishing hooks post-release  (Kilfoil et al., 2017).Furthermore, the fishing line or leader material itself may also cause abrasions pre-capture and, where hooks are retained, post-release (Whitney et al., 2017;Anderson et al., 2021).Additionally, the processes and equipment used to on board (boat angling) or land (shore angling) elasmobranchs may cause injury.Animals are often lifted out of the water onto boats.Larger fish may sometimes be lifted by the gill slits or fins, or using gaffs, with the latter in particular presenting a risk of severe injury (Musyl and Gilman, 2018).Alternative equipment, such as landing nets used to lift elasmobranchs from the water, or 'tail ropes' used to secure sharks boatside by the caudal peduncle, have the potential to cause more minor injuries, such as skin abrasions (Bansemer and Bennett, 2010).Similarly, shore anglers may cause injuries by dragging elasmobranchs up beaches, (Shiffman et al., 2017;Mohan et al., 2020;Shiffman, 2020;Weber et al., 2020;Binstock et al., 2023).Finally, a factor which has received substantial attention in teleosts, but is far less studied in elasmobranchs, is the depth change (and associated pressure and temperature changes) to which fish may be subjected during capture.While elasmobranchs lack a swim bladder, there is evidence to suggest that capture from greater depths in commercial fisheries may still cause barotrauma related injuries (depth range: 746-1913 m; Endicott and Agnew, 2004;900-1100 m;Rodríguez-Cabello and Sánchez, 2017).Additionally, elasmobranchs may also be exposed to rapid and substantial changes in water temperature (potentially > 10 • C; Fiedler, 2010) when retrieved from mesopelagic waters (200-1000 m depth), passing through the thermocline, to the sea surface.However, such extreme depth ranges may only be relevant to specialized deep water anglers, with similar studies from more representative depth ranges for recreational angling currently lacking.Given the wide range of potential injuries associated with various fishing practices within both commercial fisheries and the recreational angling sector, physical condition scores have often been used to characterize the overall physical status of elasmobranchs at the point of capture (e.g.Gurshin and Szedlmayer, 2004;Whitney et al., 2017;Musyl and Gilman, 2018).Physical condition is usually scored on a basic level from 'healthy' to moribund or dead animals (Laptikhovsky, 2004;French et al., 2015a;Hyatt et al., 2016), while also frequently including several categories for injury severity (Gurshin and Szedlmayer, 2004;Campana et al., 2009).It is important to note that such scores are both qualitative and subjective and hence may be subject to individual bias (e.g.Campana et al., 2009).

Biochemical-related impacts
While less easily observed than physical injuries, recreational angling can induce a range of biochemical disruptions in elasmobranchs (Figure 1), as shown by changes in concentrations of various biochemical indicators (e.g.Danylchuk et al., 2014;Whitney et al., 2017;Weber et al., 2021).Many of these disruptions may stem from the energetic demands associated with the process of capture and/or hypoxemia induced by emersion (air exposure) during handling.However, marked increases in body temperature during emersion have also been documented (Wosnick et al., 2018;Harding et al., 2022), while increases in body temperature may also occur, at least in regionally endothermic shark species, due to extreme activity levels during capture (Otway, 2020).Although currently underexplored, capture from greater depths may also cause body temperature increases, given water temperatures at the surface generally exceed those at greater depths (Rodríguez-Cabello and Sánchez, 2017;Prohaska et al., 2021).Such temperature changes have the potential to induce biochemical disruptions, including changes in the expression of heat-shock proteins (Weber et al., 2021).
Most of the biochemical parameters studied have been those which can be readily obtained from blood samples.Of these, the majority are also directly linked to energetic demands, including blood glucose (e.g.Danylchuk et al., 2014;French et al., 2015a;Prohaska et al., 2018), haematocrit (e.g.Hight et al., 2007;Brill et al., 2008;Heberer et al., 2010) and catecholamine (Hight et al., 2007) concentrations.Some parameters are more specifically linked to blood acidosis, caused by anaerobic respiration, including blood lactate, pCO 2 and pH (e.g.Kneebone et al., 2013;Whitney et al., 2017;Weber et al., 2021).Metabolic stress (oxidative and/or thermal), has also been assessed via erythrocyte heat shock protein (HSP) levels (e.g.Heberer et al., 2010;French et al., 2015a;Weber et al., 2021).Additionally, blood concentrations of several inorganic salt ions (e.g.Mg 2+ , Ca 2+ , Na + , K + ), which may be linked to numerous physiological processes, including acid-base regulation and ion transport, have also been recorded in several studies (e.g.Heberer et al., 2010;Danylchuk et al., 2014;Scarponi et al., 2021).Furthermore, Guida et al. (2016) categorized overall energy balance using adenylate energy charge (AEC) within tissue samples.A single study also noted exertional rhabdomyolysis, or the breakdown of muscle tissue, causing release of muscle fibre contents into the blood, alongside acute renal failure, in shortfin mako sharks (Isurus oxyrinchus) subjected to sustained angling bouts (Otway, 2020).The mechanisms behind many of these parameters are extensively detailed in Skomal and Mandelman (2012) and Renshaw et al. (2012).

Biochemical proxies
In an attempt to produce a more readily assessed and lessinvasive range of proxies for biochemical disruption (i.e.not requiring blood or tissue samples) a growing body of research has focussed on the use of reflex impairment indicators and/or assessments of specific behaviours, such as spiracular movement/buccal pumping and muscle tension (e.g.Gurshin and Szedlmayer, 2004;Laptikhovsky, 2004;Jerome et al., 2018).Such assessments often form individual components within overall scores, such as 'behavioural release condition scores' (BRCS) or 'reflex action mortality predictor' (RAMP) scores (Danylchuk et al., 2014;Hyatt et al., 2016).This approach has been broadly applied to teleosts (e.g.Davis, 2010;Brownscombe et al., 2017) (Danylchuk et al., 2014) or as an indicator for biochemical disturbances (Mannheim et al., 2018).Reflex impairment assessments typically involve assessment of an individual's responses to specific external stimuli, including the functioning of the nictitating membrane response, bite reflex and self-righting reflex (Danylchuk et al., 2014;Gallagher et al., 2014;Jerome et al., 2018;Whitney et al., 2021).This approach has shown promise in some studies, although to date results are still mixed, with the direct link between biochemical disruptions and subsequent reflex impairments not clear (Danylchuk et al., 2014;Gallagher et al., 2014;Jerome et al., 2018).

Post-release mortality
Mortality may be induced by angling either directly (e.g.Kneebone et al., 2013;Danylchuk et al., 2014;Sepulveda et al., 2015), or indirectly, for example due to increased predation risks (e.g.Mohan et al., 2020;Whitney et al., 2021) (Figure 1).Sub-lethal consequences may be induced, for example, by reduced feeding ability, energetic costs of injury healing and/or secondary infections (e.g.Borucinska et al., 2002Borucinska et al., , 2001)).Although such impacts may in-turn lead to delayed or indirect mortality (Adams et al., 2015;Kilfoil et al., 2017), for the purposes of this section we included only documented mortalities (both direct and indirect).Mortalities are usually identified via data-logging or telemetry devices (e.g.Moyes et al., 2006;Kneebone et al., 2013;French et al., 2015a;Whitney et al., 2017;Mohan et al., 2020).Post-release mortality is generally characterized based upon a lack of horizontal movement (Gurshin and Szedlmayer, 2004;Mohan et al., 2020), lack of transmissions (Gallagher et al., 2014) and/or static depth profiles, where an animal is assumed to be dead and resting on the seabed based on bathymetric data (Sepulveda et al., 2015;French et al., 2015a;Whitney et al., 2016Whitney et al., , 2017;;Mohan et al., 2020).In other cases mortality is inferred by tag detachment at a set maximum depth (e.g.Sepulveda et al., 2015;Domingo et al., 2018), sometimes corroborated by this exceeding the maximum recorded depth for that species (French et al., 2015a).
Post-release mortality rates associated with recreational catch-and-release angling (excluding deliberately caudal finhooked common thresher sharks, Alopias vulpinus) were identified in 14 studies, representing a combined total of 412 elasmobranch individuals from 12 species captured, with all being either Lamniform (n = 152) or Carcharhiniform (n = 260) sharks (Table 2).These ranged from 0% (5 studies with no mortalities) to as high as 100% (Binstock et al., 2023), with a mean value from all studies of 14.3% (i.e.59 total postrelease mortalities; Table 2).Overall post-release mortality rates were similar across both orders (Lamniformes = 13.8%;Carcharhiniformes = 14.6%), although the figure for Lamniformes was heavily skewed by the results of Kneebone et al. (2013), where juvenile sand tigers (Carcharias taurus) were subject to high levels of gut-hooking (42%).When this study was excluded the mortality rate for order Lamniformes was reduced to 5.7%.Similarly, great hammerheads (Sphyrna mokarran) showed by far the highest mortality rates within the Carcharhiniformes (100%; Table 2), albeit this was based upon a very small sample size (N = 2; Binstock et al., 2023).Also note that this basic comparison does not account for inter-study differences in various risk factors such as emersion, hook removal, etc.
Of the physical injury-related impacts, the most commonly identified cause for post-release mortality is physical injury caused by fishing hooks, either through hook retention, generally associated with gut-hooking (Adams et al., 2015;Kilfoil et al., 2017), or through excessive bleeding, generally caused by injuries to the gills (Gurshin and Szedlmayer, 2004;French et al., 2015a;French, 2017).As previously noted, barotrauma injuries have been recorded in commercial fisheries, with longline capture from greater depths linked to reduced survival rates of Raja sp.anon (depth range: 746-1913 m;Endicott and Agnew, 2004) and deep water shark species (depth range 900-1100 m; Rodríguez-Cabello and Sánchez, 2017).However, the relevance to recreational angling at shallower depths is unknown.Conversely, angling from the relatively shallower depths associated with shore angling may also pose greater mortality risks (Weber et al., 2020;Binstock et al., 2023), with these potentially linked to injuries associated with lifting or dragging of animals out of the water and onto beaches, jetties, rocks or piers and/or to greater biochemical disruptions stemming from longer air exposure periods or prolonged restraint in relatively warm and shallow coastal waters.
As might be expected, moribund health scores and severe injuries have mostly been found to represent strong predictors for subsequent post-release mortality (Campana et al., 2016(Campana et al., , 2009;;Musyl andGilman, 2019, 2018), although not in all cases (French et al., 2015a;Domingo et al., 2018).Less severe categories are generally poorer predictors (Hyatt et al., 2016;Domingo et al., 2018;Anderson et al., 2021), although with some exceptions (Musyl andGilman, 2019, 2018)  barring a few exceptions (e.g.Gurshin and Szedlmayer, 2004;Whitney et al., 2017), most such studies have been performed within commercial longline fisheries (e.g.Campana et al., 2009;Musyl and Gilman, 2018;Bowlby et al., 2020), where injuries, typically under industrial, harvest-oriented settings, are often more severe than in recreational angling settings.Thus, the more severe categories (and best predictors of mortality) may have limited relevance to recreational angling.Additionally, the high subjectivity of such observations can mean that variability in categorization among observers may overwhelm any biological differences (Campana et al., 2009).
Of the numerous biochemical measures studied, the most consistently reliable predictor of mortality has been blood lactate concentration (e.g.Moyes et al., 2006;Renshaw et al., 2012;Whitney et al., 2021), although this may partly relate to the relative abundance of studies recording lactate levels.This pattern likely relates to the availability of portable blood analysers (e.g.i-STAT, Lactate Pro), initially designed for human use, which have been adopted as rapid and relatively accurate ways to determine blood pH and lactate levels (Awruch et al., 2011;Harter et al., 2015).Nevertheless, in studies where multiple haematological variables have been measured, blood lactate has consistently emerged as among the strongest predictors of post-release survival/mortality (Moyes et al., 2006;Whitney et al., 2021).

Chronic health impacts
Although not subject to extensive research and, hence, generally only reported incidentally, some long-term chronic impacts have been reported for elasmobranchs subjected to both recreational and commercial hook and line fishing, with almost all of these linked to hook retention (Figure 1).In this instance comparisons can be cautiously made between recreational angling and commercial fisheries, for which a much greater body of research exists, given the impacts of retained hooks are likely to be similar, irrespective of the specific fishing method (although less animal welfare conscious attempts to remove hooks in commercial fisheries may cause more severe injuries, even where hook removal is unsuccessful; Bansemer and Bennett, 2010;Campana et al., 2016).Several studies on post-release survival of both recreationally and commercially caught elasmobranchs have reported which individuals had retained hooks, with some then correlating these with post-release mortality rates (e.g.Kneebone et al., 2013;French et al., 2015b;Kilfoil et al., 2017).Borucinska et al. (2002) noted that retained hooks identified in 6 captured blue sharks (Prionace glauca) led to severe and chronic health problems, including damage to various internal organs, in all cases, while Mucientes and Queiroz (2019) reported severe damage to the oesophagus of a shortfin mako shark due to a retained hook.Adams et al. (2015) also reported the cause of death for a shortfin mako shark as being due to a retained hook, with Kilfoil et al. (2017) reporting the same for a sand tiger.

Effects on parturition
An additional impact of both recreational and commercial fishing for elasmobranchs, which has received surprisingly little attention, and for which the specific cause(s) and physiological mechanisms remain unknown, is the effect of capture on parturition.Capture-induced parturition, or abortion, has been directly reported for at least 89 live young bearing elasmobranch species within 27 families, (Adams et al., 2018;Wosnick et al., 2019).Although most of these examples came from commercial fisheries (Adams et al., 2018;Wosnick et al., 2019), several miscellaneous reports and social media posts indicate that capture-induced parturition/abortion also occurs as a result of recreational angling (Adams et al., 2018).Adams et al. (2018) also cautioned that the current scarcity of such reports may be due to parturition being unobserved, rather than infrequent, as parturition may occur prior to landing or post-release.Both Wosnick et al. (2019) and Adams et al. (2018) noted that neonates rarely, if ever, survived, irrespective of the development stage, following capture-induced parturition.Thus, this phenomenon may represent an important cryptic effect of recreational catchand-release angling, particularly if pregnant females represent a substantial proportion of the catch.Furthermore, although the relevance to recreational angling is unknown, capture of pregnant elasmobranchs in trawls may lead to other negative effects on parturition, including reduced neonate size, as observed for southern fiddler rays (Trygonorrhina dumerilii) (Guida et al., 2017).

General (handling & equipment)
Likely the most studied determining factors for fisheries impacts in both commercial fisheries and recreational angling are the choice of hook-type and the removal or non-removal of fishing hooks at the point of capture, with these two factors often intrinsically linked.Although there are a multitude of different 'hook-types' available to recreational anglers, these can usually be simplified to one of the two most common hook-types; the traditional j-hook and the circle-hook, so named due to their profile.Additionally, some circle-hook designs may have a hook point which is at an offset angle, rather than in line with the hook shank, with some anglers preferring these due to a perceived higher catch rate.While most fishing hooks also include a barb after the hook point, 'barbless' hooks are also available, although the use of barbed or barbless hooks has received surprisingly little attention within the field of elasmobranch research, despite evidence that they can reduce unhooking times and aid in hook removal for teleosts (reviewed in Cooke and Sneddon, 2007).Across all fishing methods, most studies have indicated a reduced risk of gut-hooking and increased chance of jawhooking with the usage of circle-hooks (Afonso et al., 2011;Pacheco et al., 2011;French et al., 2015a;French, 2017;Keller et al., 2020), as well as a lower risk of foul-hooking (i.e.hooking outside the mouth), which has also been linked to mortality (Heberer et al., 2010;French et al., 2015a;French, 2017).These findings are further supported by meta-analyses of commercial longline data (Godin et al., 2012;Reinhardt et al., 2018;Keller et al., 2021).Reinhardt et al. (2018) noted lower at-vessel mortality for 3 shark species (oceanic whitetip, Carcharhinus longimanus; shortfin mako, Isurus oxyrinchus; and scalloped hammerhead, Sphyrna lewini) when circlehooks were used, while Godin et al. (2012)  overall, use of circle-hooks corresponded with a significant decrease in gut-hooking and at-vessel-mortality.However, when considering the conservation benefits of circle-hook usage, some cautionary points should be noted.Firstly, offset point circle-hooks may cause higher gut-hooking rates than non-offset circle-hooks (Rice et al., 2012).Additionally, retained circle-hooks may take longer for some species to shed compared to j-hooks, with one study noting that retained j-hooks were shed by pelagic stingray (Pteroplatytrygon violacea) within 6 days (n = 6), while circle-hooks took an average of 44.5 days to be shed (n = 4) and up to 125 days (François et al., 2019).
Similarly to hook-type, the practices of either removing hooks or cutting the line or wire leader material above hooks (i.e.causing hook retention) has also been relatively wellstudied.As previously noted, retained hooks may cause severe and chronic health effects (Borucinska et al., 2002(Borucinska et al., , 2001;;Adams et al., 2015), while trailing fishing line may also have negative effects, such as tissue necrosis (François et al., 2019).However, studies on teleosts indicate that, in some cases, hook removal may actually be detrimental to survival due to greater emersion periods (Cooke and Wilde, 2007;Wilde and Sawynok, 2009), with one study on post-release survival of longline-caught shortfin mako sharks indicating this may also be the case for some elasmobranch species (Domingo et al., 2018).Hook removal from gut-hooked elasmobranchs may also be difficult or impossible without causing severe injury to the animal (Kilfoil et al., 2017).
Where fishing hooks are retained by the animal postrelease, hook location may be a critical factor in determining post-release outcomes, with hook retention in gut-hooked elasmobranchs linked to chronic and sometimes fatal health problems (Borucinska et al., 2002(Borucinska et al., , 2001;;Lécu et al., 2011;Adams et al., 2015) and both increased short-and longterm mortality rates (Campana et al., 2009;Kilfoil et al., 2017).In contrast, where retained hooks are located in the outer part of the jaw, negative impacts such as tissue necrosis may be less severe, although still an issue in some cases (Bansemer and Bennett, 2010).Begue et al. (2020) noted that tiger sharks with (in some cases multiple) externally visible retained fishing hooks shed these within 6 months on average and appeared to be largely unaffected, in terms of feeding ability, growth, reproduction and tissue necrosis.Likewise, Chin et al. (2015) noted that blacktip reef sharks (Carcharhinus melanopterus) also appeared to be extremely resilient to visible retained fishing hooks.
Given the difficulties sometimes associated with hook removal in elasmobranchs, the choice of hook materials may be key to reducing chronic impacts.Corrodible hooks are more likely to be quickly shed, as shown by Begue et al. (2020), who compared 50% hook retention probabilities in tiger sharks for corrodible (5.7 months) and stainless steel (7.8 months) hooks.Indeed, use of corrodible hooks is mandated in some commercial longline fisheries (NOAA, 2003).However, Begue et al. (2020) speculated that, in some cases only the external portion of the hook may be lost, with the internal proportion remaining.Horst (2000) also speculatively hypothesized that corrosion of such hooks might lead to greater tissue damage, and thus lower survival, due to galvanic action.It should also be noted that all hooks will eventually corrode, but at different rates and with different lag times depending on the material thickness and type of anti-corrosive coating used.
Another factor which has received substantial attention is the time spent between hooking and landing a shark or ray, often termed as 'fight time', in some cases also reported inclusive of handling time, although these two capture stages involve different stressors and thus such studies should not be considered directly comparable (e.g.Skomal and Chase, 2002;Danylchuk et al., 2014 ;Shea et al., 2022).Fight time relates to a complex combination of angler and fish behaviour, fish size and energy status and fishing equipment, including line class and drag setting (McLoughlin and Eliason, 2008;Cooke et al., 2013;Danylchuk et al., 2014;French, 2017;Kilfoil et al., 2017), as well as species-specific factors, with protracted fight times reported both anecdotally and experimentally for lamnids and great hammerheads (French et al., 2015a;French, 2017;Anderson et al., 2021).Thus, it may be difficult to disentangle these numerous interlinked factors, particularly given the small sample sizes often used in such studies (e.g.Danylchuk et al., 2014;French et al., 2015a;Shea et al., 2022), potentially contributing to the null effects seen in some studies (Danylchuk et al., 2014;Shea et al., 2022).However, despite these difficulties, several studies have reported significant biochemical effects from increasing fight times (e.g.Kneebone et al., 2013;French, 2017;Whitney et al., 2017;Weber et al., 2021), although no survival impacts have yet been documented.
Differences in emersion periods and comparison of airexposed versus non-air-exposed elasmobranchs have been studied via both recreational angling and commercial fisheries, as well as experimental emersion studies.In general, study results have followed a pattern of increased biochemical disturbance, longer recovery times and/or decreased survival following emersion (Cicia et al., 2012;Murray et al., 2015;Bowlby et al., 2020Bowlby et al., , 2021)), or with longer emersion durations (Dicken et al., 2006;Cicia et al., 2012;Murray et al., 2015), although Weber et al. (2021) found that emersion changed the primary mechanism of blood acidosis (i.e.respiratory vs. metabolic) but not the degree of acidosis experienced by rod-and-line caught blacktip sharks.It should be noted that emersion durations in lab and commercial fishery studies often far exceed what would be expected in a recreational angling setting (Laptikhovsky, 2004;Cicia et al., 2012;Mandelman et al., 2013;Lambert et al., 2018).Even recreational angling-based studies may involve non-representative emersion periods due to the need to obtain measurements, biological samples and/or apply data-logging packages.Conversely, changes in angler behaviour in the presence of scientists or participation of the most conservation-minded anglers in such Both water and air temperature appear to play a role in the severity of catch-and-release impacts.Higher water temperatures are well known to reduce survival in teleosts (reviewed in Gale et al., 2013), while several studies have indicated that this may also hold true for elasmobranchs (French et al., 2015a;Whitney et al., 2017;Knotek et al., 2022;Binstock et al., 2023).The temperature change associated with emersion may also have an effect, with greater disparity between water and air temperatures shown to cause changes in elasmobranch surface body temperature, which may be greater in smaller individuals (Wosnick et al., 2018;Harding et al., 2022), and with acute thermal shock during emersion also shown to induce additional biochemical disturbances (Cicia et al., 2012).Surprisingly little research attention has been paid towards the landing and handling practices for elasmobranchs, as well as the usage of various types of assisting equipment to on board or land them or secure them at the boat side to enable, for example, hook removal, measurement, tagging and/or photography.This is despite the injury risks associated with equipment, such as gaffs (Musyl and Gilman, 2018) and tail ropes (Bansemer and Bennett, 2010), and with practices, such as dragging sharks up beaches (Shiffman et al., 2017), or misplacement of body ropes around the head and gill area (Mohan et al., 2020).The lack of such studies may relate to the relatively recent timing of most catch-and-release studies, with usage of gaffs in particular increasingly rare among some groups of anglers practicing catch-and-release (French, 2017;French et al., 2019b).However, gaffs may still be used in some angling communities, even where elasmobranchs are frequently released (Dicken et al., 2006;Lynch et al., 2010;French et al., 2019b).Similarly, other related factors, such as specific handling methods for shore and boat anglers, or for dealing with more vulnerable species or pregnant females, have received little or no research attention, despite many angler best practice guides covering these topics (Authors, pers.obs.).
It has been hypothesized by several authors that a key factor influencing mortality rates from all methods of hook and line capture may be the relationship between a species' behavioural response to capture and its aerobic scope, defined as the difference between minimum and maximum oxygen consumption rates (Clark et al., 2013), with a greater aerobic scope leading to reduced blood acidosis and thus less severe post-release effects (e.g.Marshall et al., 2012;Skomal and Mandelman, 2012;French et al., 2015b).There is limited information available on the metabolic rates for most elasmobranchs; however, lamnid sharks are often hypothesized to possess a higher aerobic scope than carcharhinids, owing to regional endothermy (Marshall et al., 2012;French et al., 2015b).This has been hypothesized as being a major contributor to their relatively high post-release survival (French et al., 2015b;Anderson et al., 2021), despite often pronounced behavioural responses to capture (e.g.French et al., 2015b;Otway, 2020;Anderson et al., 2021).It should however be noted that the regional endothermy and prolonged fight times of some lamnids may contribute to biochemical disruptions not experienced by other elasmobranchs, including exertional rhabdomyolysis Otway (2020).
In contrast to the lamnids, carcharhinid sharks are hypothesized to possess a lower aerobic scope and may hence utilize anaerobic respiration to a greater extent during bouts of increased activity (Mandelman and Skomal, 2009), leading to greater biochemical disruption for a given activity level.The behavioural responses of carcharhinids to capture appear to vary widely, albeit much of the available data come from commercial fisheries so it is not clear how such patterns may translate to recreational angling.Longline and drumline based studies have recorded subdued behavioural responses in nurse sharks (Ginglyostoma cirratum) and tiger sharks (Galeocerdo cuvier) versus comparatively extreme responses in blacktip sharks (Carcharhinus limbatus) and great hammerheads (Mandelman and Skomal, 2009;Gallagher et al., 2017bGallagher et al., , 2014;;Bouyoucos et al., 2018).Correspondingly, great hammerheads and blacktip sharks caught using such methods have been found to be subject to severe biochemical disturbances and reflex impairments and very high at-vessel and/or post-release mortality (e.g.Mandelman and Skomal, 2009;Gallagher et al., 2014;Jerome et al., 2018), while sympatric tiger sharks have much lower mortality rates (Mandelman and Skomal, 2009;Gallagher et al., 2014).The results of Binstock et al. (2023) also suggest a similar pattern in shore-based recreational fisheries, with blacktip and great hammerhead sharks subject to far higher post-release mortality rates than sympatric bull sharks (Carcharhinus leucas) or tiger sharks (Table 2).Furthermore, anecdotal reports from recreational anglers also support these observations regarding both the behavioural response to capture and poor post-release survival in great hammerheads (McClellan Press et al., 2016).
The relative risk posed by hypoxemia during handling is also likely to vary greatly between species, based on respiratory mode, metabolic rate and hypoxemia tolerance, although this has received only limited attention (Cicia et al., 2012), with comparative studies currently lacking.Hypoxemia may be more readily induced in ram-ventilating species compared to species which perform spiracle-or buccal pumping, potentially even without emersion, due to reduced water flow over the gills (McLoughlin and Eliason, 2008;Dapp et al., 2016;Aalbers et al., 2021).This may be an issue when sharks are restrained alongside a boat (e.g.Sepulveda et al., 2015;Shea et al., 2022) or held stationary in shallow water at beaches (e.g.Shiffman et al., 2017;Hingley, 2020).There is evidence to suggest that capture-induced hypoxemia may be mitigated by pumping water over a shark's gills (Davie et al., 1993), albeit this study was carried out using sharks under tonic immobility.The outcomes of hypoxemia may not be immediate (i.e.at-vessel-mortality), with a potential for post-release effects such as respiratory acidosis, which may compound metabolic acidosis from struggling on the line (Weber et al., 2021), resulting in post-release mortality or prolonged recovery periods (e.g.Renshaw et al., 2012;Murray et al., 2015;Bowlby et al., 2020).Post-release mortality may also occur in ram-ventilating species if exhaustion prevents adequate gill ventilation (Dapp et al., 2016).
Individual species or genera may have specific feeding or hunting behaviours which place them at a greater risk of severe recreational fishing-related impacts (Heberer et al., 2010;Sepulveda et al., 2019Sepulveda et al., , 2015;;Aalbers et al., 2021).For example, thresher sharks (Alopias spp.) are often (both deliberately and accidentally) foul-hooked in the tail due to their specific feeding behaviour, where they use their elongated upper caudal lobe to stun prey (Heberer et al., 2010;Sepulveda et al., 2015).This can lead to increased mortality (up to 26%; Heberer et al., 2010) as the sharks are unable to ram-ventilate when retrieved tail-first.In this case, usage of circle-hooks is extremely effective in preventing tail hooking, thereby reducing mortality rates (Heberer et al., 2010;Sepulveda et al., 2015).In contrast, the gulp feeding mechanism of sand tigers may result in high rates of guthooking, irrespective of the hook-type used (Kneebone et al., 2013;Kilfoil et al., 2017) and thus mitigation may be challenging or impossible.
The results of studies investigating the effects of inter-and intra-specific body size differences in a recreational angling setting have been mixed, with the body of research on this topic currently limited.A number of commercial longlinebased studies have indicated that biochemical disturbances and at-vessel-mortality may decrease with increasing individual size (e.g.Diaz and Serafy, 2005;Braccini and Waltrick, 2019;Bowlby et al., 2021).However, recreational anglingbased studies have reported both concurrent (Whitney et al., 2017;Shea et al., 2022) and contrasting results (Heberer et al., 2010;Scarponi et al., 2021).In species which exhibit pronounced behavioural responses to capture, larger individuals may experience prolonged fight times, leading to greater biochemical disruption (Heberer et al., 2010).Alternatively, the relatively greater glycogen stores of larger individuals may lead to lower biochemical disruption (Jerome et al., 2018), with this potentially offsetting any additional energy expenditure in species where behavioural responses to capture are less pronounced.

Current research limitations and knowledge gaps
Catch-and-release science has become an increasingly hot topic within elasmobranch research, as evidenced by a marked increase in the publication rate of such studies in the last 10 years.However, much of the current research has focussed on the orders Carcharhiniformes (23 catch-and-release studies identified) and Lamniformes (12 studies).In contrast, we identified relatively few studies on the orders Rajiformes (4 studies), Rhinopristiformes (3 studies) and Orectobliformes (1 study).Other elasmobranch orders, including Squaliformes and Squatiniformes, were not found to be represented by any catch-and-release studies.Even within the two most studied orders most research has focussed on only a handful of commonly targeted species.The lack of studies on rajids in particular may have important conservation implications, given many rajid species are commonly targeted by recreational anglers.Currently most knowledge on capture-related effects for rajids comes from commercial trawling studies, where fishing and handling practices differ greatly from recreational angling (e.g.Laptikhovsky, 2004;Arlinghaus et al., 2007;Enever et al., 2009;Mandelman et al., 2013).To our knowledge, only a single study has investigated postrelease behavioural impacts relating to recreational fishing for rajids, with this study unable to assess post-release survival as data-logging packages had to be physically recovered from recaptured flapper skates (Dipturus intermedius) (Lavender et al., 2022).From a management perspective this makes it impossible to accurately determine angling impacts where no species-, family-, or even order-specific mortality rates have been documented.
From a practical perspective, when choosing biochemical indicators to predict post-release outcomes, the current body of evidence strongly indicates that blood lactate concentration is the best predictor for post-release mortality or survival (e.g.Moyes et al., 2006;Renshaw et al., 2012;Whitney et al., 2021) and carries the additional advantage of being relatively easy to assess using portable blood lactate analysers.However, the high degree of inter-specific variation in blood lactate concentrations, even between closely related or congeneric species (Marshall et al., 2012;Renshaw et al., 2012;Gallagher et al., 2014), presents an issue.Hence, accurate prediction of post-release mortality would likely require determination of species-specific lactate mortality thresholds.Similarly, when using physical condition scores to characterize physical status of animals, differences in the weighting of health scores may hamper inter-study comparison.We suggest that consideration be given to adopting a standardized scoring system to minimize such issues.various telemetry and/or data-logging device based studies providing a substantial body of research on the shortmedium term ( 1 month) post-release mortality rates for a range of elasmobranch species (e.g.Danylchuk et al., 2014;Sepulveda et al., 2015;French et al., 2015a).In contrast, there has been comparatively little research on long-term consequences of recreational angling, such as those stemming from hook retention.Beyond the obvious expense and difficulty associated with prolonged monitoring periods, any assessment of the wider population-level impact is also likely to be hampered by a lack of available information on the rates of hook retention for most recreational fisheries targeting elasmobranchs.Most reported hook retention rates come from experimental studies (e.g.Kneebone et al., 2013;Danylchuk et al., 2014;Kilfoil et al., 2017), where researcher and/or volunteer angler behaviour may differ from that of typical recreational anglers, or from small subsets of specific angling communities where similar caveats may apply (Dicken et al., 2006;McClellan Press et al., 2016), meaning the overall risk posed by this behaviour is difficult to reliably quantify.This pattern also highlights a broader lack of information on angler behaviour, with studies to date covering only a small number of specific angling groups and species, and with angler behaviours varying widely between these (e.g.McClellan Press et al., 2016;Shiffman et al., 2017;French et al., 2019aFrench et al., , 2019b)).When combined with the lack of data on how angler behaviours such as hook removal affect mortality rates, this makes predicting the population-level impact of specific angler behaviours near-impossible.

Considerations for best practice advice to anglers
While current understanding of many of the animal welfare considerations noted above is limited, and substantial knowledge gaps remain for many taxa, there is sufficient evidence from recreational angling studies, with some inferences made from commercial and ex-situ studies, to provide several key recommendations to the angling community.

Angling practices
When taken together, research findings show that gut-, gilland foul-hooking result in higher mortality rates from both direct hooking injuries, and from either extended emersion periods and unhooking injuries where hooks are removed, or from chronic health impacts if hooks are retained postrelease.In comparison, jaw-hooking may ease unhooking (potentially eliminating the need for emersion), lead to fewer unhooking injuries and a higher likelihood of hook removal, and result in fewer negative impacts if hooks are retained.Therefore, the usage of non-offset, barbless circle-hooks and, where possible without causing further injury, removal of hooks before release, are key steps to reduce both lethal and chronic sub-lethal effects of recreational angling.Additionally, use of corrodible hooks may reduce the long-term impacts of retained hooks.Furthermore, the choice of landing equipment also has the potential to greatly impact injury risks for elasmobranchs.The use of gaffs should be avoided, given the potential for severe injury.Similarly, tail ropes should only be used where necessary and should ideally be constructed from a low friction rope material to minimize skin damage.
Beyond reducing physical injury, the most beneficial practices appear to be those which can reduce the level of respiratory or metabolic acidosis and other biochemical disturbances experienced by an animal during and after capture.Although recreational angling specific data are limited, there is clear evidence demonstrating that emersion is a significant stressor for elasmobranchs and should thus be minimized or eliminated if possible, to maximize survival likelihood.Likewise, irrespective of the difficulty in detecting such effects, there is evidence to suggest that reducing fight times will reduce mortality risks in elasmobranchs, with such benefits likely to be most easily achieved by use of appropriately rated fishing gear, including use of lines of relatively higher breaking strain, thus allowing increased resistance to be applied using reel drag settings.While the level of conservation benefit associated with these practices is likely to vary based on respiratory mode, aerobic scope and behavioural responses to capture, the overall pattern of reduced biochemical disturbance with reduced fight times and emersion appears to hold true across most, if not all, elasmobranch species studied.Furthermore, cognisance should be given to water and air temperatures during angling, with higher temperatures likely to induce greater biochemical disturbances, particularly where animals are removed from the water.Finally, specific animal welfare considerations should be made for species or genera which may carry a higher risk of post-release mortality, such as hammerheads, thresher sharks and sand tigers, and for pregnant females, given the potential for capture-induced effects on parturition.

Human dimension
Consideration of the potential impact of the various recommendations outlined above must consider the correlation (or lack thereof) between scientific research, angler guidance and real-world changes in angler behaviour.Best practice advice is only likely to have conservation benefits if paired with effective research dissemination and education/outreach programmes targeted towards the recreational angling community.A prime example of this can be seen in the United States, where anglers wishing to fish for sharks in US federal waters of the Atlantic, Caribbean and Gulf of Mexico must complete a short online training course to obtain the relevant federal permits, with this course outlining best practices for shark angling, as well as the identification of prohibited shark species which cannot be landed for conservation reasons.A major barrier to improving angler behaviour regarding animal welfare may be an overall lack of knowledge on the conservation status of many elasmobranch species within the angling community, as well as the belief that recreational angling has little to no impact on elasmobranch populations  (Gallagher et al., 2015;Shiffman et al., 2017).Therefore, the decline in many elasmobranch populations must be articulated to anglers and their role in this identified, so that they can amend any unwitting and potentially injurious practices which may result from unfamiliarity about the conservation status of some species and the potential impact of their actions.Anglers can act responsibly when practicing catchand-release, with case studies demonstrating high levels of willingness to implement conservation-minded behaviours in parts of Australia (Heard et al., 2016).Therefore, successfully engaging with anglers and further alerting them to the risks posed by-and the likely benefits of avoiding-injurious practices is likely to have a tangible benefit in maximizing elasmobranch welfare and conservation outcomes.
As a case-study demonstrating the importance of angler engagement, one issue which must be addressed by scientists is the view among some anglers that circle-hooks reduce shark or ray catchability, with this likely to act as a key barrier to angler adoption (Serafy et al., 2012).In contrast to this, numerous studies on longline fisheries and recreational angling have indicated that circle-hooks have either a null or non-significant effect on catch rates (Gulak and Carlson, 2021;Keller et al., 2020;e.g. Yokota et al., 2006), as backed up by meta-analyses of commercial data (Godin et al., 2012;Keller et al., 2021).A few studies have also reported significant positive effects (Afonso et al., 2011;Foster et al., 2012;Hannan et al., 2013), while, to our knowledge, no studies have reported large negative impacts on catch rates.In a recreational angling context, Willey et al. (2016) reported higher hooking and capture rates with circle-hooks for 10 shark species.This perception among anglers therefore represents an inability by scientists and fisheries managers to effectively communicate this near-consensus of results to the angling community.

Conclusions
Elasmobranch catch-and-release science is a rapidly growing research field, with continual advancements in our overall knowledge as new research findings are published.This rate of progress notwithstanding, there are several taxonomic groups which have received little to no research attention, despite many species within these being targets for anglers.Hence, there is a clear need to better match research effort to those species most likely to be impacted by the recreational angling sector.Additionally, better standardization of the variables recorded during catch-and-release studies, such as physical condition scores, may aid inter-study comparison.Such an approach may ultimately enable quantification of combined mortality risks, using the most reliable physical and biochemical mortality predictors, for the most commonly captured species, upon which recreational angling may have the greatest impact.
Based on the literature reviewed here, several key recommendations for best practice stand out.These are likely unsurprising to those involved in recreational angling-based research; however, the empirical data provided here help to underline their importance.In brief, these include the use of corrodible, non-offset, barbless circle-hooks and removal of these where possible, use of appropriately rated fishing gear to minimize fight times, rapid unhooking and release of captured elasmobranchs without removal from the water and avoidance of handling practices or equipment (e.g.gaffs) likely to cause injury to captured elasmobranchs.Such recommendations are only of value if followed by anglers, with angler engagement being key to compliance.Engagement with the angling community may be best improved by provision of angler forums/workshops, led primarily by trusted angling 'personalities', in addition to online and physical resources, as this enables guidance to be tailored to individuals and allows anglers' queries and concerns to be addressed directly.Such an approach would also better facilitate species-specific education and guidance where native species are particularly vulnerable to angling-related impacts, their populations are threatened or in decline, their conservation status is not well known among anglers, and/or they may require specific handling procedures or equipment.
Where a more robust approach is required to meet conservation objectives, regulatory bodies should consider the implementation and enforcement of restrictions or total bans on targeting of vulnerable and poor conservation status species, such as great hammerheads.While comparable regulations governing capture of such species are in place in some areas, such as the US state of Florida, there is strong evidence to suggest these, and similar legislation for other large sharks may be ignored by many anglers fishing illegally (Shiffman et al., 2017) or legally circumvented by keeping sharks in the water (Kilfoil et al., 2017).It may also be necessary to implement temporary fishery closures during periods of extremely high water temperatures, with this likely to be of increasing relevance given current climate projections.Similarly, consideration should be given to implementation of temporary fisheries closures around parturition periods, as is commonplace for many teleosts (e.g.salmonids), particularly where pregnant females, and especially those of threatened and/or declining species, represent a large proportion of elasmobranch catches.

Table 2 :
Sepulveda et al. (2015)uding post-release mortality rates by species and order ( * mortalities fromSepulveda et al. (2015)are reported inclusive of mouth-hooked sharks only, i.e. excluding caudal fin-hooked sharks; * * For one of the individuals the suspected mortality occurred 14 days post-capture and could not be reliably confirmed, however the pattern of behaviour was considered indicative of mortality)